1. Field of the Invention
The present invention relates to an image processing device and an image processing method.
2. Description of the Related Art
It is known that, in imaging devices such as still cameras and video cameras, light transmitted through a lens is affected by a point spread function (PSF) associated with each color, which causes point images to spread. Further, the degree of dispersion of the PSF increases as an image height increases. Note that the image height is a value that expresses, for example, the image position on an imaging surface of an imaging element as a distance from an optical axis.
FIG. 3A to FIG. 3C are graphs each showing a point spread function. The graph in FIG. 3A shows the PSF on the optical axis. The graph in FIG. 3B shows the PSF of the image height 50%. The graph in FIG. 3C shows the PSF of the image height 100%. The chain line indicates a green component, the solid line indicates a red component, and the broken line indicates a blue component. In FIG. 3A to FIG. 3C, the horizontal axis represents the position in an image height direction and the vertical axis represents light intensity.
As shown in FIG. 3A to FIG. 3C, the PSF of each color has the characteristics that, as the image height increases, magnification chromatic aberration increases and at the same time, the spread (hereinafter also referred to as “PSF distortion”) in a flared portion of the PSF shape increases. Further, in the examples shown in FIG. 3A to FIG. 3C, the flared portion spreads and elongates to the right. In this manner, the PSF distortion has an asymmetrical shape in the image height direction, and one-sided blur occurs.
FIG. 4A is a graph showing an example of a PSF in which one-sided blur does not occur. FIG. 4B is a graph showing an example of a PSF in which one-sided blur does occur. The chain line indicates a green component, the solid line indicates a red component, and the broken line indicates a blue component. In FIG. 4A, one-sided blur does not occur in the red component (R), the blue component (B) and the green component (G), and coloring due to the one-sided blur does not occur.
In comparison with the PSF of FIG. 4A, the one-sided blur occurs in the red component (R) and the blue component (B) in the PSF of FIG. 4B. In addition, there is an area in which the pixel level of the red component (R) or the blue component (B) exceeds the pixel level of the green component (G) (the area enclosed by the ellipse in FIG. 4B). As a result, a color (purple), which ideally should not appear, appears on an imaging surface of an imaging element, and the color that should not appear is applied to a subject image. A false color on the fringe etc. is generated because of the above-described reason, and thus image quality deteriorates.
Note that the direction in which the one-sided blur occurs (for example, whether it occurs on the right side or occurs on the left side) varies depending on lens characteristics, focus, zoom and exposure states.
A method for correcting PSF distortion is disclosed in Japanese Patent Application Publication No. JP-A-2000-92318, for example. In order to correct the PSF distortion, for example, a deconvolution method such as that described in Japanese Patent Application Publication No. JP-A-2000-92318 has been proposed. Further, Japanese Patent Application Publication No. JP-A-2003-18407 discloses a technology that eliminates color bleeding at image edges.